Code EO37, Manifold Air Temperature (Mat) Sensor Too High: Notes

The MAT sensor measures the air temperature in the air cleaner box and relays this information to the ECM. The ECM applies and monitors a 5-volt signal to the sensor. The sensor is a thermistor that changes its internal resistance as its temperature changes.

When the sensor is cold (internal resistance high), the ECM will see a high signal voltage. This the ECM relates to a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the ECM will relate the lower voltage to a warm engine.

As the intake air temperature increases, the sensor resistance becomes less, and the voltage drops.

Code EO37 will set if a signal voltage indicates manifold air temperature about 275°F (135°C), and the vehicle is traveling over 40 MPH for over 16 seconds. Possible causes of a Code EO37 are: Faulty wiring or terminals, circuit 472 shorted to ground, shorted MAT sensor, or a faulty ECM.

Manifold air temperature is one of the inputs used to control: Fuel delivery, spark timing (EST), knock control (ESC), and idle speed (IAC).

1. If the opposite failure mode (open sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter ED05. With the opposite failure created, parameter ED05 should display a "MAT" reading of -35 to -40°C. To create an open sensor signal, disconnect the MAT sensor connector. If the "MAT" reading is now -35° to -40°C, the ECM and the wiring harness are okay. The fault must be in the MAT sensor itself.
2. If the "MAT" reading is -34°C or warmer, then there is a short to ground in the wiring harness or the ECM.